django评论框架:distinct()不起作用? [英] django comment framework: distinct() does not work?

问题描述

在注释模型的任何字段上运行distinct()总是返回所有记录，

Comment.objects.values('user').distinct()

[{'用户':1}，{'用户':0}，{'用户':0}，{'用户':0}，{'用户':0}， {'用户':1}，{'用户':1}，{'用户':1}，{'用户':1}]

Comment.objects.values('ip_address').distinct()

[{'ip_address':u'127.0.0.1'}，{'ip_address':u'192.168.0.180'}， {'ip_address':u'192.168.0.180'}，{'ip_address':u'192.168.0.180'}， {'ip_address':u'192.168.0. 180'}，{'ip_address':u'192.168.0.180'}， {'ip_address':u'192.168.0.180'}，{'ip_address':u'192.168.0.180'}， {'ip_address':u'192.168.0.180'}]

为什么会这样?有没有解决的办法?谢谢！

PS:在我的测试过程中，distinct()在自定义模型的不同类型的字段中运行得非常好.评论框架有什么特别之处吗?

结论点 谢谢大家回答这个问题，再加上一些阅读，我得出以下结论:

1. values()影响最终结果的SELECT部分​​中的查找字段 sql("<​​a href="https://docs.djangoproject.com/zh-CN/1.3/ref/models/querysets/#values" rel="noreferrer"> values()采用可选的位置参数* fields 指定SELECT应该限制的字段名称)
2. order_by()也将其参数添加到SELECT部分​​.

3. 在查找中使用distinct()将导致sql看起来像这样:

   选择 DISTINCT [fields1，fields2，fields3]从...位置...

   和字段的值共同决定记录是否唯一.这些字段可能来自查找中的values()或order_by()函数.

4. 因此order_by()添加了一些不必要的效果当与distinct()结合使用时，order_by中指定的字段也要考虑到记录是否唯一

5. 默认情况下，Django Comment具有一个隐藏的order_by参数，从而引发了整个问题.任何模型在返回qs时都具有隐藏的order_by可能导致相同的问题.

6. 解决该问题的方法是通过在末尾添加一个空的order_by() 查找，这将删除默认的order_by.

解决方案

Comment.objects.values('user').distinct().order_by()

Running distinct() on any field of the comment model always returns all the records,

Comment.objects.values('user').distinct()

[{'user': 1}, {'user': 0}, {'user': 0}, {'user': 0}, {'user': 0}, {'user': 1}, {'user': 1}, {'user': 1}, {'user': 1}]

Comment.objects.values('ip_address').distinct()

[{'ip_address': u'127.0.0.1'},{'ip_address': u'192.168.0.180'}, {'ip_address':u'192.168.0.180'}, {'ip_address': u'192.168.0.180'}, {'ip_address': u'192.168.0. 180'}, {'ip_address': u'192.168.0.180'}, {'ip_address': u'192.168.0.180'}, {'ip_address': u'192.168.0.180'}, {'ip_address': u'192.168.0.180'}]

Why is this happening? Is there a way around this? Thanks!

ps: distinct() does run very well in different types of fields of a custom model during my test. Something special about the Comments framework?

Bit of conclusion Thanks everybody answering this question, combined with some reading I get conclusion as following:

1. values() influences the lookup fields in SELECT part of the final sql("values() takes optional positional arguments, *fields, which specify field names to which the SELECT should be limited")
2. order_by() adds its parameter to the SELECT part as well.

3. using distinct() in a look up will result the sql to look like this:

   SELECT DISTINCT [fields1, fields2, fields3] FROM ... WHERE...

   and the values of the fields all together decides whether a record is unique. The fields may come from values() or order_by() functions in the lookup.

4. So the order_by() is adding some unwanted effects when combined with distinct(), the fields specified in order_by is also take into consideration whether a record is unique

5. Django Comment has a hidden order_by parameter by default, thus creating the whole problem. Any model has a hidden order_by when returning the qs can cause the same problem.

6. The way of solving it is by adding an empty order_by() at the end of the lookup, which removes the default order_by.

解决方案

Comment.objects.values('user').distinct().order_by()

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